The present invention relates to telephone networks, and more particularly to a system and method for accessing, monitoring and testing electrical circuits on a telecommunication multi-service transport system.
The telephone industry has changed drastically since the divestiture of the Bell System. Today, several regional Bell Operating Companies (RBOCs) and independent telephone companies provide local telephone service within an excess of 100 Local Access Transport Areas (LATAs). These companies are forced to rely on interexchange carriers such as AT&T, MCI and Sprint for transmission of calls from one LATA to another. The responsibility for quality and performance of the telephone circuit is thus split between local telephone companies and interexchange carriers.
Currently, new technologies and equipment are needed which will allow service providers to rapidly respond to traffic and service needs in the metro environment, while reducing their power consumption, equipment space requirements and overall cost. To this end, several leading equipment vendors have announced new telecommunication provisioning platforms termed Multi-Service Transport Platforms (MSTP) which integrate multiple technologies into a single box replacing older, larger, and less integrated technologies such a Add-Drop multiplexers (ADM) and digital cross connect systems (DCS).
While the MSTP's are advanced, all Network Elements (NE) mentioned above rely on the same Synchronous Optical Network (SONET) and Synchronous Digital Hierarchy (SDH) protocols. While integrating more capabilities and functions into the new telecommunication provisioning platforms such as the MSTP's, the basic low level architecture of the older telecommunication provisioning platforms remains the same in the new MSTP equipment. In particular, the platforms use standardized DS1 and DS3 provisioning line cards interchangeable between several vendor's platforms to aggregate asynchronous analog telephone lines. They also use the traditional service restoration schemes utilizing protection cards (redundant working cards) and fiber ring architecture. As an example, the MSTP's may be connected to SONET/SDH bidirectional line switched rings (BLSR). This type of SONET/SDH architecture delivers scalable, highly reliable ring architecture with dual counter rotating rings delivering two unique paths per pair of interconnected nodes. As there are always two available paths, one is designated as working (active) and the second as the protect (secondary) in standby mode. Similarly in the telecommunication multi-service transport system, there exists a working (active) line card for each DS1 or DS3 circuit as well as a protection card held in a standby mode in case a working card fails and the circuit must be restored. The protection cards may be configured 1:1, one protection card for each working card, or 1:N where there is one protection card for N working cards. Each DSx card is comprised of expensive circuitry which provides an interface between the legacy asynchronous side of the telecommunication network with higher speed synchronous SONET/SDH side of the telecommunication network. Typically each DSx line card includes circuitry for a LIU (line interface unit), a framer, a mapper and bus interface.
DS3 (and to a lesser extent DS1) signals carry large amounts of data per unit time and represent a considerable financial investment on the part of the end user, for whom bandwidth is expensive as it has become for the operating company facility planner. The operating company using DS3 runs the risk of a substantial outage in the case of a crippling impairment or total failure of such high-speed digital facilities. Those who manage the DS3 facilities of both end users and service providers are thus quite interested in the performance of the digital links in their networks. They are not satisfied to let the circuit performance information embedded in the formatted bit streams they deal with simply pass by without extracting data which can be quite useful in managing the network and in minimizing the costly impact of service outages.
To this end, several approaches have been attempted to extract this performance information from the DS1 or DS3 (DSx) signals from the telecommunication multi-service transport system. One test access method entails connecting test equipment to the dedicated DSx test access service ports. The circuit to be tested is then cross connected to the dedicated DSx test access service ports through the STS1 or VT1.5 switching fabric. The drawback to this method is that the dedicated test access service ports are occupying ports which otherwise could carry revenue generating traffic. Secondly, these ports are usually on the rear side of the MSTP equipment making it inconvenient to perform the test access when needed.
A second test access method involves making test access through the central chassis. This method requires the central chassis to have dedicated DSx ports, an extra DSx framer, and extra data bus to pass data from DSx test access ports on the central chassis to the STS1 or VT1.5 switching fabric. This method also requires an extra bus to be connected between the chassis and the switching fabric in order to connect to the chassis ports. The drawback to this method is that it is very expensive due to the extra DSx framer and extra data bus required.
Since an MSTP can function like a mini DCS with transport capability, it is desirable to have test access capability so that electric circuit (e.g., DS1 or DS3 card) tests can be performed. Not only a test access must be provided, it has to be an economical way for providing such a test access using a system which is essentially transparent to in-service DSx lines and paths, thereby providing non-intrusive surveillance and performance monitoring.
Desirable in the art of telephone network designs are additional methods with which better and more economical access, monitoring and testing of telecommunication multi-service transport system can be achieved.